A modern automobile is provided with numerous safety devices having the function of preserving the physical safety of the occupants in the event of accidents. One of the most widespread safety devices is the airbag, which comprises a flexible cushion that is inflated in very short times in the case of collision (detected by accelerometric sensors) thanks to a small explosive charge.
Some international standards envisage that an airbag set in a front position must not be activated when a baby is present on the front seat. For this reason, it is necessary to know whether a baby is present on the front seat. Said indication can be supplied in different ways, amongst which the most common is the presence of a switch that disables entry into action of the airbag and that is driven by means of a lock actuated by the starting key of the vehicle.
However, said solution is not deemed fully reliable in so far as it requires intervention of the driver, who must manually disable/re-activate triggering of the airbag. For this reason, alternative solutions have been proposed, amongst which we may recall use of proximity sensors to evaluate the “dimensions” of the passenger present on the seat, use of radiofrequency recognition systems (transponders or the like) for determining the presence of a cradle (which must be provided with a transponder or the like), or else use of weight sensors to determine the weight of the passenger present on the seat.
For example, the U.S. Pat. No. 6,366,200 describes a system designed to detect the weight of the passenger present on the seat by means of a set of weight sensors for determining whether the seat is empty, whether it is occupied by a baby, or else whether it is occupied by an adult; in particular, the seat is considered as being empty if the weight detected by the weight sensors is less than a first threshold value; the seat is considered as being occupied by an adult if the weight detected by the weight sensors is higher than a second threshold value; finally, the seat is considered as being occupied by a baby if the weight detected by the weight sensors is comprised between the first threshold value and the second threshold value.
In airbags currently available on the market, the internal pressure and volume of the inflated cushion are constant and determined a priori. Recently, a new generation of airbags (referred to as “smart airbags”) has been proposed, which can be controlled so as to partialize inflation of the cushion and hence obtain a variable internal pressure and/or volume of the inflated cushion. In particular, the internal volume and/or pressure of the inflated cushion are/is varied as a function of the violence of the impact and/or as a function of the weight of the occupant of the seat and/or of other parameters, so as to adapt the characteristics of the cushion to the morphological characteristics of the occupant of the seat. An example of a “smart airbag” is provided by the U.S. Pat. No. 6,532,408.
From what has been set forth above, it is clear that it is necessary to provide a mounting system of the seat equipped with a device for measuring the weight of the occupant.
The documents U.S. Pat. No. 6,039,344, WO0100454 and EP142624 describe a mounting system with measurement of the weight of the occupant for a seat of a motor vehicle, in which a seat is slidably mounted on a slide guide, which is in turn supported by a top frame. The top frame is mounted in a floating way on a bottom frame rigidly connected to the bodywork of the motor vehicle by means of interposition of four weight sensors.
The known mounting systems with measurement of the weight of the occupant described above present the drawback of requiring a high constructional precision (i.e., very small constructional tolerances) for guaranteeing proper operation. Said high constructional precision inevitably entails long production times and high manufacturing costs.
U.S. Pat. No. 4,765,423 discloses an adaptor for load cells with through loading holes (primarily cylindrical or doughnut type) used in multiple cell applications (scales); it provides lateral stops and anti-tipping control for the associated load receptacles.